Molecular Simulations of Water Vapor Adsorption in Hygroscopic Polymer-Solvent Mixtures*

Advanced polymer-based desiccants have the ability to adsorb water vapor for dehumidification and atmospheric water harvesting applications. Molecular simulations are conducted to study water vapor adsorption in pure polyacrylamide and polyacrylamide-glycerol mixtures. Molecular dynamics and Monte Carlo simulations are used to elucidate the coupling behavior between vapor adsorption and polymer chain structures at 298 K. The polymer chain conformations, radial distribution functions, and pore size distributions in the polymer are analyzed to understand the effects of glycerol and water on plasticizing the polyacrylamide. The effects of adsorption induced swelling is seen to have a large effect on the adsorption isotherms of polymer systems, especially in the higher relative humidity range. The addition of glycerol leads to the polyacrylamide to have a more swollen initial state before adsorption and enhance vapor adsorption due to its high hygroscopy.